Electron discharge device



M y 8, 1935. 'v. o. ALLEN ELECTRON DISCHARGE DEVICE V GAME/v ATTORNEYPatented May 28.1935 f 7 t -Bi nca' memcance I 2,002,653 I r LECTRONDISCHARGE DEvIoE 4 Victor 0. Allen, Madison, N. J., assignor, bymesnehassignments, .to Radio Corporation of America, a corporation ofDelaware a v V j Application May a4, 1930, Serial K 2155397 h h k achime.(011250-275) 1 This invention relates to electron dischargedeutilized effectively as an electron emitter between vices, and withparticularity to so-called indithe ranges of SQO" centigradeand 800centigrade rectly heated emittersforaudions or similar deandabovethelatter temperature'the chromium vices. g J g material with which thecaesiumi'smixed prevents 5 A principal object of the invention istoprothe volatilization or other liberation of the 6 vide an-indirectlyheated cathode for audionsand casium. i similar devices which has aminimum of time One preferred manner of manufacturing the lag'betweenthe application of heating current coating is as follows: finelydivided'met'allic and the effective emission of electrons. chromiumisthoroughly mixed with a casium salt 10 Another object of the inventionis to provide such as" caesium 'dich'romate and with a suitable 10 7 anelectron emissive coating for audions or the binder to form a liquidemulsion which is sprayed like have 'a high electron emission at acomparaonto the surface in the usual manner. When the tively lowtemperature. a cathode thus coated is mounted within the audion Anotherobject of the invention is to employ and the latter is subjected to theusual heat treat- 1 an electron emitting cathode for audions or the mentduring the evacuating process the heat 15 like employing caesium. 1 7causes a reaction between the chromium and the A feature of theinvention relates to the method caesium salt wherebyfree caesium isproduced and of applying an electron emitting coatingcontainthe chromiumsalt is changed to chromium oxide. ing caesium to a cathode orsimilarielementsuch It will of course be understood that instead of asordinarily employed in electron discharge deeffecting this change duringthe evacuating proc- 20 vices. V -ess that the emulsion as sprayed onthe cathode A further feature relates to an indirectly heated surfacemay be heated to produce the chemical cathode for audions or the likewhich has a minireaction whereby caesium and chromium oxide mum ofheatinertia. are produced, prior to the actual mounting of the Otherfeatures and advantages not specifically cathode within the audion orother device. 25

enumerated will be apparent afteraconsideration Referring to the drawingthere is shown one of the following detail descriptionsand theappreferredmanner of constructing an electron pended claims. a vemitting cathode embodying the features of the While the element caesiumhas been known to invention. The numeral I represents a rod of possesselectron emitting properties when subceramic insulating material havinga pair of 30 I jected to heat heretofore this'element has notlongitudinal boresZ and 3whereinthe heater wire found any commercialapplication in audions or 4 is looped and supported. As shown, the opthelike because of the difiiculty of controlling posite sides of the rod lare cut away to provide its emissivity. This is due mainly to the factthat staggered notches 5 whereby the heater wire cesium has a very lowvaporizing temperature aisexposed at spaced intervals. Surrounding the35 and consequently it is extremely difiicult to apply rod I is a sleeve6 of metal such as nickel or. the the caesium and maintain it on thecathode surlike, carrying the coating (containing the casium face. Thisis particularly true in so-called indiand chromium oxide as hereinabovedescribed. rectly heated cathodes where the electron The ends ofthesleeve 6 are preferably left un- 40 mit i mat r a is usu ra d t a" y1 ncoated. When the terminals of the wire 4 are 40 drical n Smooth surfaceusually known as the connected to a source of heating current the sleevecathode Sleeve- 6 is heated due to heat transmitted through the It hasfoundthat 3533mm m rod I, as well as due to the heat radiated directly'Ployed pracmcany as an electron mutter-by from the exposedportions ofthe-wire 4; Thus bining it with compound mixture contain; the rod Icombines the advantages of ha g the ing chromium. It has also. beenfound that I a chromium oxide in a nascent condition has the reqmslteheat mema as Well enablmg the v sleeve 6 to be'directly heated byradiation. For $5315; srglfl gdfslogrblirliegafifitgaiigg 331 115362111;1353 5 t i description of the method of forming the i cathode filamentat temperatures above 800 rod I reference yb had to appilcaiwn senal 50centigr'ade 1; the Same m the caesium is No. 441,703. As hereinabovedescribedthe-coattained in the mixed condition with the chromium ing 7 m1 1 the form of an emulsioncontaincompound or compounds and is capableof being" in metallic c om m x dwith & ce m S rendered electronicallyactive at temperatures such as caesium dichromate or the above describedas low as 300. In other wordsthe caesiu'mis emulsion may be sprayed onthe sleeve 6 and sub- 5 je cted to heat to reduce the caesium and tooxidize the chromium as hereinabove described.

Audions employing cathodes such as that disclosed are capable of givingthe requisite high emission at temperatures as low as. 300 centigradeand accidental overloads on the heater filae ment do not seriouslyvolatilize or liberate the caesium from the cathode surface.

While one specific type of heater'co'nstruction' is shown in thedrawing; it will be understood that the invention is not limitedthereto, the broad aspect of the invention residing in the method ofemploying and producing caesiumdn va practical way to render it usefulin audi'o'nsor similar electron discharge devices: 7

Further, it will be understoodthat the invention is not limited to theparticula'r'materials disclosed and that various changesand-modifica;-,;

tions may be made without departing from the spirit and. scope of theinvention. T 1 'What isclaimed is: Y g l w v '1. An electron emitting;cathode for audions and similar devices includingf'a member coated withcaesium-bearing material s "and, chromium,

said" caesium bearing material'being capable of reduction by chromium toproduce chromium oxide. 1

2. Anelectron emittinggcathode for audions and similar devicescomprising a member having acoating of metallic caesium'and, chromiumoxide.

3. A'mixture for preparing an electron emissive member comprisingmetallic chromium and caesium dichromate. g

4. In an electron emitter for vacuum tubes the combination of a rod ofinsulation having a longitudinal bore therethrough and a plurality ofundercut notches, exposing said bore at spaced intervals, a heaterwire-threaded through said bore, a metallic sleeve surrounding said rodand an electron emissive coating containing caesium and amaterialcontaining chromium on the exterior surface of said sleeve.

- 5,.;The step in-the method of manufacturing an 'emissive cathode forelectron discharge devices which comprises mixing caesium di-chromatewith comminuted chromium, applying the resultant mixture to -a cathodesupport, and subjecting the devices comprising a member-having a coatingof caesiumcompound which is electronically acwhole to heat treatment toreduce the caesium 7 compound to the metal caesium.

6.-' An emitting cathode for audions or similar .vIcToao. ALLEN. g

